This invention relates to a WDM (wavelength division multiplexing) optical transmission system and, in particular, to an optical ADM (add-drop multiplexing) node and an optical cross-connect node (i.e., an optical path switching node) used in the WDM optical transmission system.
In each of Japanese Unexamined Patent Publications (JP-A) Nos. 3-214936 (214936/1991) and 6-37717 (37717/1994), disclosure is made of an optical repeater for repeating a WDM optical signal having a main signal component (channel) and a monitor/control signal component different in wavelength from the main signal component. In particular, the latter publication teaches to use the monitor/control signal component in carrying state information representative of a normal or abnormal state of the optical repeater.
Conventional WDM optical transmission systems include a point-to-point system, an optical ADM ring system, and an optical cross-connect system. In the point-to-point system and the optical ADM ring system, each optical ADM node holds channel information such as xe2x80x9cwhich channel is to be separated (dropped)/inserted (added)xe2x80x9d, xe2x80x9cwhich node a separated channel has passed through?xe2x80x9d, and xe2x80x9cwhich node an inserted channel is to be transmitted to?xe2x80x9d. In accordance with the information, control is carried out.
In the optical cross-connect system also, each optical cross-connect node (i.e., optical path switching node) holds channel information such as xe2x80x9cwhich node a passing channel has passed through?xe2x80x9d and xe2x80x9cwhich node each channel is to be transmitted to?xe2x80x9d. In accordance with the information, control is carried out.
The above-mentioned conventional WDM optical transmission systems can not flexibly deal with modification of the destination of each channel and modification of the separated/inserted channel.
In order to achieve the effective use of transmission paths and the flexibility, a variable channel structure is preferred rather than use of a fixed channel (wavelength) assigned to each node. The variable channel structure requires an information transfer arrangement for transferring the above-mentioned channel information. However, such information transfer arrangement is not defined as yet.
It is therefore an object of this invention to provide an optical ADM apparatus (optical ADM node) capable of implementing a WDM optical transmission system (point-to-point system or optical ADM ring system) in which a monitor/control signal component is used in carrying control information for a main signal component (channel).
It is another object of this invention to provide a WDM optical transmission system using the above-mentioned optical ADM apparatus (optical ADM node).
It is still another object of this invention to provide an optical path switching apparatus (optical cross-connect node) capable of implementing a WDM optical transmission system (optical cross-connect system) in which a monitor/control signal component is used in carrying control information for a main signal component (channel).
Other objects of this invention will become clear as the description proceeds.
According to an aspect of this invention, there is provided an optical ADM (add-drop multiplexing) apparatus responsive to a WDM (wavelength division-multiplexed) optical signal comprising first through n-th (n being an integer not less than 2) main signal components different in wavelength from one another and a single monitor/control signal component different in wavelength from each of the first through the n-th main signal components, wherein:
the monitor/control signal component carries first through n-th monitor/control signals which represent origination apparatus identifiers of origination apparatuses of the first through the n-th main signal components and destination apparatus identifiers of destination apparatuses of the first through the n-th main signal components in correspondence to the first through the n-th main signal components;
the optical ADM apparatus comprises:
a divider for dividing the WDM optical signal into the first through the n-th main signal components and the monitor/control signal component;
a monitor/control signal terminator coupled to the divider for terminating the monitor/control signal component to produce the first through the n-th monitor/control signals;
a monitor/control signal processor connected to the monitor/control signal terminator for producing, when the destination apparatus identifier represented by one of the first through the n-th monitor/control signals is coincident with an identifier of the optical ADM apparatus, a specifying signal specifying, as a specified main signal component, one of the first through the n-th main signal components that corresponds to the one of the first through the n-th monitor/control signals, the monitor/control signal processor further producing the first through the n-th monitor/control signals with the origination apparatus identifier corresponding to the specified main signal component rewritten into the identifier of the optical ADM apparatus and with the destination apparatus identifier corresponding to the specified main signal component rewritten into a different apparatus identifier of a different apparatus which is different from the optical ADM apparatus;
an ADM unit coupled to the divider and connected to the monitor/control signal processor for dropping, when receives the specifying signal from the monitor/control signal processor, the specified main signal component from the first through the n-th main signal components and for producing, when receives a new main signal component equal in wavelength to the specified main signal component, the first through the n-th main signal components with the new main signal component added as the specified main signal component;
an ADM terminal station coupled to the ADM unit for receiving the specified main signal component from the ADM unit and for transmitting to the ADM unit the new main signal component equal in wavelength to the specified main signal component;
a monitor/control signal component generator connected to the monitor/control signal processor for producing the monitor/control signal component which carries the first through the n-th monitor/control signals produced by the monitor/control signal processor; and
an optical combiner coupled to the ADM unit and the monitor/control signal component generator for producing another WDM optical signal comprising the first through the n-th main signal components produced by the ADM unit and the monitor/control signal component produced by the monitor/control signal component generator.
Preferably, the monitor/control signal processor produces, when each of the destination apparatus identifiers represented by the first through the n-th monitor/control signals is not coincident with the identifier of the optical ADM apparatus, a pass signal and for transmitting to the monitor/control signal component generator the first through the n-th monitor/control signals with the identifier of the optical ADM apparatus added to each of the first through the n-th monitor/control signals as an intermediate apparatus identifier.
In this event, the ADM unit further has a function of transmitting, when receives the pass signal from the monitor/control signal processor, the first through the n-th main signal components from the divider to the optical combiner as they are.
According to another aspect of this invention, there is provided an optical path switching apparatus responsive to a WDM (wavelength division-multiplexed) optical signal comprising first through n-th (n being an integer not less than 2) main signal components different in wavelength from one another and a single monitor/control signal component different in wavelength from each of the first through the n-th main signal components, wherein:
the monitor/control signal component carries first through n-th monitor/control signals which represent, in corrrespondence to the first through the n-th main signal components, intermediate apparatus identifiers of intermediate apparatuses through which the first through the n-th main signal components are passed;
the optical path switching apparatus comprising:
a divider for dividing the WDM optical signal into the first through the n-th main signal components and the monitor/control signal component;
a monitor/control signal terminator coupled to the divider for terminating the monitor/control signal component to produce the first through the n-th monitor/control signals;
a monitor/control signal processor connected to the monitor/control signal terminator for producing, on the basis of the intermediate apparatus identifiers represented by the first through the n-th monitor/control signals and an identifier of the optical path switching apparatus, a specifying signal specifying next apparatuses to which the first through the n-th main signal components are to be delivered, respectively, and for producing the first through the n-th monitor/control signals with the identifier of the optical path switching apparatus added to each of the first through the n-th monitor/control signals as the intermediate apparatus identifier;
a monitor/control signal component generator connected to the monitor/control signal processor for producing the monitor/control signal component which carries the first through the n-th monitor/control signals produced by the monitor/control signal processor; and
an optical path switch coupled to the divider and the monitor/control signal component generator and connected to the monitor/control signal processor for transmitting first through n-th WDM optical signals comprising the first through the n-th main signal components and the monitor/control signal component from the monitor/control signal component generator, respectively, to the next apparatuses specified by the specifying signal supplied from the monitor/control signal processor, respectively.